Load development question (Update Post #8 with more questions)

[thump_rrr]

HI purchased a Savage 10BA (24" barrel 1 x 10" twist) as my first precision rifle nearly 2 months ago.
I bought a box of Sierra 180gr SMK's and some Varget and set out to develop an accurate load.

The Sierra manual shows a max load of 41.7gr of Varget which produced 2500fps.
I started at 37.5 gr and worked my way up to 41.7 gr looking for pressure signs and comparing accuracy.

At 41.5gr I had 1/5 rounds make the bolt slightly sticky.
It wasn't enough to need me to even use my palm but my fingers felt a difference. The primer wasn't flattened and there was no case bulge etc. so I proceeded in firing the 5 rounds of 41.7 gr.

2 of the 5 rounds produced a sticky bolt with one of them needing me to use my palm to tap the bolt up with a slight effort.

I determined that 39.9 and 41.1 gr were my most accurate loads and left it at that.

On Saturday I purchased a chronograph and decided that I'd go to the range and test some of my loads.

My 9mm IPSC load came in slightly higher than expected at an average of 1160 fps but not too far off. My .45 IPSC load came in at an average of 750 fps which is normal.

When I got to my .308 load of 41.1 gr it averaged at slightly over 2600 fps.
This is over 100 fps faster than the 41.7 gr max load published in the Sierra manual and this was with 0.6 gr less powder and a 2" shorter barrel.

What could be the reason for such a difference over published data?
I would suspect lot to lot variances to be less than that.

Brass was Federal as was used in the Sierra test.
Primers were CCI large rifle ( they used Federal)
2.005" trim length
2.800" OAL (0.020" off the lands actual measurement)
Primer pockets were uniformed and flash holes deburred.
Powder was weighed on my Lymann 1500XL and scale was verified before and after with RCBS check weights.

 

[rral22]

What you experienced is not unusual. Every gun is an individual and will react differently to any specific recipe you find - or it may react just as predicted.

That is the fact of reloading. That is why you always start low and work up, paying attention to everything. It is also why a chronograph is a very useful (and relatively cheap) tool for any reloader.

All I can say is - your testing has shown you something about your gun with those specific components, from those specific lots, when loaded using your specific techniques.

 

[H4831]

Not all rifles are born equal!
At one time I had two 30-06 rifles. A load that was fine in one, caused a sticky bolt on the other. They could both shoot about the same maximum velocity, but there was sometimes nearly 2 grains eifference in the powder, between the two.
I had two 243 rifles that were exactly the same. I had a good, safe load in one, but that same load loosened the primer on the first shot, with the other rifle.
At least you now know why your bolt was starting to get sticky, and it was good observance on your part, to pick it up right away.

 

[MHouser]

Does the sierra manual really say max = 41.7. The hodgdon data center shows it as being a lot higher than that. Even the 190gr are listed at min=41 and max=44. I use 43 in my savage with 180gr and 24" barrel /wo issue. Good job you are working up loads.

 

[stocker]

As well as the differences between rifles that H4831 related my experience with low end chronographs is less than confidence building. My Chrony consistently reads higher velocity than a couple of others I have tested at the same time with the same loads. The results with mine were also considerably higher than published data at the same loading with no indication of higher pressure. Knowing that I adjust my readings somewhat when I use it. If you have a top end chronograph like an Oehler the results are dependable most often.

 

[horseman2]

Carmichael did a test with two rifles with consecutive serial numbers and both performed differently in velocity and accuracy. My 700 in .280 remington will take two grains more powder that max loads listed and it has a short throat.

 

[vviking]

Unusual results can also come from unexpected causes.

One time a 6.5mm Swede expanded its Lapua cased primer pocket, with very conservative start loads.
The problem?.
Heavy(two thousanth's) fouling build up in the leade/throat area.
That cupro-nickle jacket stuff is diabolical to remove!.

Electronic scales can go wonky, without any indication they have gone inaccurate.
In my case, the Dillon was affected by flourescent light ballast interference. The reading would stay consistent while the actual charge varied plus/minus 1/2 grain, or more.
Wore out a new 6.5/06 barrel chasing that gremlin.
All is now good, the RCBS 10/10 balance beam scale having proved absolutely trustworthy.

Chrony's do vary. Have seen up to 400fps difference in readings ... with the same loads in the same gun, but on different days/atmospheric conditions. Those outings where one gets more than the usual "error", being most likely suspect.

Good on you OP, for your awareness and prudence.

 

[thump_rrr]

Went back to the range today with a bunch of different loads.
All were loaded with 40.0 gr in Winchester brass this time.
The brass was already fire formed by this rifle so I only neck sized.
I tried different OAL's from 2.800" to 2.820" (touching the lands) in 0.005" incriments.
Temperature was 55F and the wind was gusting to 20mph blowing towards 1 o'clock.
My best groups were between 0.55 MOA and 0.67 MOA between 100m and 170m.

The problem I'm having is that my bolt feels like it's sticking not on the lift but when I go to pull it back.
None of the rounds had any difficulty closing the bolt.
The next question is can this brass still be neck sized or do I need to bump the shoulders back a few thousands?

My fired brass reads 1.624 on my Hornady headspace gauge which seems shorter than the .308 specification of min. 1.630 yet the rounds pass being dropped into my Dillon headspace gauge.

Thanks in advance

 

[vviking]

1/2 to 5/8 MOA in gusty conditions is nothing to sneeze at!. Nice shooting.

Sounds like you may have a rough chamber.
High Pressure is felt first on the bolt lift. You stated that is not happening at your 40gr load.
Once cammed back to full bolt lift, the case will normally slide free from a smooth, round chamber.
A rough chamber can resist initial bolt pull.
Take a good close look at the fired brass, with a magnifying glass. Faint drag marks and/or burnishing will be there if this is indeed your problem.

No need to shoulder bump your brass if the bolt closes without undue effort.

As for your headspace readings, I wouldn't worry, as long as you know
those cases don't have excess headspace in that chamber.

Chambers can be polished.